The general election campaign between President Biden and former President Trump, the rematch almost nobody wanted, began ahead of schedule last week.

Former South Carolina Gov. Nikki Haley is still contesting the Republican nomination, but she will need a miracle — actually, more than one miracle — to dethrone Trump.

The chairwoman of the Republican National Committee, Ronna McDaniel, declared the former president to be her party’s presumptive nominee even though only two states have actually voted in caucuses or primaries.

In practice, Biden and Trump are campaigning against each other as if Haley were already gone.

This indecently early start isn’t the only factor that makes this election unusual:

It has been 112 years since an incumbent president and a former president collided in a rematch. Never in modern history have two candidates so unpopular gone up against each other (although the 2016 contest between Trump and Democrat Hillary Clinton came close). And never before have the presumptive nominees been so old; Biden is 81, Trump will turn 78 in June.

“The fact that you have two [candidates who’ve been president], neither of whom is well-liked, makes it a unique situation,” Democratic pollster and strategist Mark Mellman said.

When an incumbent president runs for a second term, the election is normally a referendum on his record.

But this will be a “dual referendum,” because both candidates have recent records to defend.

Biden is viewed unfavorably by 58% of Americans and Trump by 57%, according to a recent Gallup Poll.

Many voters will choose by deciding which unappetizing candidate to vote against, not which champion to vote for.

That’s especially true for one key subset: the roughly 15% of Americans who dislike both candidates, often called “double haters.”

The double haters helped determine the outcome in both 2016, when most of them chose Trump over Clinton, and 2020, when most deserted Trump for Biden.

The combination of a dual referendum and dual unpopularity guarantees that this will be one of the most negative campaigns in memory.

“Both sides want to make the election a referendum on the other candidate. That will push the campaign to be negative,” Mellman noted.

It’s already started.

Trump’s message has focused on the damage he claims Biden has inflicted on the country: high inflation, surges in undocumented immigration, rising crime. (Inflation is easing, the economy is growing, and the FBI’s statistics show crime dropping, but that won’t stop the former president from repeating his claims.)

Biden’s message has focused on the damage he says a second Trump presidency would do: the erosion of democracy, tougher restrictions on abortion, deeper economic inequality.

Neither has presented much in the way of a positive vision. Both campaigns are focused on fear, not hope.

“This could be the most depressing nine months ever in terms of public discourse,” Republican pollster David Winston predicted.

Here’s what the two candidates need to do to win, according to strategists from both parties:

“Trump’s team needs to keep the focus and the pressure on Biden, to make the election a referendum on his record,” Mellman said. “They also need to reassure people about Trump’s faults and foibles — which is hard to do, because Trump constantly reminds people of his faults.”

Republican strategists say Trump needs to spend less time complaining about the 2020 election, which he wrongly claims was stolen. Those grievances mobilize Trump’s already-loyal supporters, but they alienate the moderate voters and “double haters” who will decide the election.

Biden, meanwhile, “has to do two big things,” Mellman said. “One is to communicate more effectively what he has accomplished,” because “people are largely unaware” of what he’s done.

“Second, he has to make clear the downsides of choosing Trump. Yes, it’s about democracy, but it’s about much more than that.”

Biden started in on that priority last week when he spoke at an abortion rights rally in Virginia.

Aides say the president also intends to lay out a positive agenda for a second term in his State of the Union address on March 7.

“Question No. 1 is: How is someone who dislikes both candidates going to choose?” Winston said. “They want to hear candidates discuss solutions to problems. They don’t want to hear a battle of grievances.”

Head-to-head polls suggest that if the election were held tomorrow, Trump would win a narrow popular-vote victory.

But nine months before election day, those polls are not reliable predictions. Much can change between now and November.

If the economy continues to improve, that should help Biden. If Trump is convicted in one of the criminal trials he faces, that might help Biden too. International crises could cut either way.

Third-party candidates — including Robert F, Kennedy Jr., Green Party candidate Jill Stein, and the wild-card organization No Labels — could draw votes from both candidates.

One more wild card: the elderly candidates’ health. A major medical event on either side could tip the election.

However uninspiring the campaign may be, the stakes remain enormous.

Biden and Trump offer starkly contrasting futures: an old-school Democrat who has moved gradually toward the left, and an autocratic Republican populist who says he will use the presidency to prosecute his opponents.

And the outcome remains unpredictable. This month’s polls can’t forecast how voters will feel in November.

So don’t believe anyone who claims to know how it will come out. They don’t.